Patellar Tendon–Lateral Trochlear Ridge Distance Measurement as an Indicator of Patellar Instability With Malalignment

Background: There exist multiple radiographic measurements to assess patellar instability and maltracking. While originally described as a measurement predictive of patellar instability, patellar tendon-lateral trochlear ridge distance (PT-LTR) has not yet been explored as an indicative measurement of patellar maltracking in the setting of instability. Purpose: To assess PT-LTR in patients with instability with and without concomitant malalignment to determine whether PT-LTR may be a significant measurement in patients who exhibit patellar maltracking in addition to patellar instability, as well as to explore the relationship between patellar height and tibial tubercle-trochlear groove distance (TT-TG) to PT-LTR. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Three groups were studied, with 30 patients included in each group: (1) patients with an anterior cruciate ligament (ACL) tear without a history of patellar instability who underwent ACL reconstruction (ACLR) (control group or ACLR group), (2) patients who underwent isolated medial patellofemoral ligament reconstruction (MPFLR) for patellofemoral instability (MPFLR group), and (3) patients who underwent combined MPFLR and tibial tubercle transfer (TTT) for patellofemoral instability (MPFLR+TTT group). Intraclass correlation coefficients (ICCs) were generated to determine level of agreement in PT-LTR measurement between raters. Appropriate statistical tests were utilized for analysis. Results: < .0001). Measurements for the ACLR, isolated MPFLR, and MPFLR+TTT groups were 1.15 ± 3.71 mm, 6.60 ± 6.58 mm, 12.72 ± 8.43 mm, respectively. When comparing all patients, those with patella alta, an elevated TT-TG, and a combination of both had higher PT-LTR than patients without patella alta or elevated TT-TG. Conclusion: The mean PT-LTR was significantly higher in patients who underwent MPFLR+TTT compared with that in ACLR controls and patients who underwent isolated MPFLR. This may reflect its role as a measurement of patellar maltracking in the setting of patellar instability. PT-LTR may be a useful tool in predicting which patients with instability may benefit from a concomitant bony realignment procedure in addition to a soft tissue stabilization procedure.